Decomposition of sodium aluminate liquor



Aug. 22, 1944. H. TIEDl-:MANN

DECOMPOSITION OF SODIUM ALUMINATE 'LIQUOR original Filed oct. 2, 1940 New ATTO RN El tions is usually carried-out in Patented Aug. 2,2, 1944 DECOMPOSITION F SODIUM ALUMINATE Hans Tiedemann, Akasaka-ku, Tokyo, Japan; vestedin the Alien Property Custodian Original application'October 2, 1940, Serial No.

395,350. Divided and this application October i 30, 1941, Serial No. 417,204. In Germany December 21, 1937 3 Claims. (Cl. 23-285) The present invention'refers-to a process and apparatus for the lproduction of aluminumhydroxide. y

'I'he presentapplic'ation has been divided out from my co-pending U. S. patent application, Ser. No. 359,350.

By the well known Bayer method sodium alu-` minate solutions are prepared from bauxite and caustic soda; after hydrate of alumina has been added as Lnooulator these solutions'are stirred forv three to six days whereby 50 to 60% of the alumina is precipitated as hydrate due to hydrolytic action.

This decomposition of sodi aluminate solugh steel tanks oi 5 to 8 meter diameter and 8 to 12 meter height which. are provided' with agitator mechanisms supported'on vertical shafts.

These unusually large agitator tanks require huge investment and foundation costs and require Vlli a considerable power for their operation. Usually they have to be operated discontinuously which represents a further disadvantage as the subsequent steps of the process lcan be done con-l ?tinuously.

It is an object of this invention to avoid the aforesaid disadvantages and to obtain a continuous and speedy precipitation and production of aluminumhydroxide from aluminate liquors. It is a further object of the inventionto greatly simplify the equipment for stirring-out the aluminate liquor and to reduce at the-same time the costs of-installation and of operation.

It is a further object of the invention to feed and to transport the aluminate liquor through a combined reaction or precipitationand a subse- In this way a .partial circulation of the liquor is created in the tank by which a part of the kformed `particles of hydrate of alumina is continuously -carried back towards the feed whereby the precipitation is accelerated. l

A further advantage' of the present-invention consists therein that the precipitated particles of hydrate of alumina can be settled in a quiet zone i subsequent to the reaction zone from which they.,

can be easily removed.

' In ylarge installations several of these longitudinal basins can becombined to one basin with` proper partitions in between. The retention time ofthe solution can be varied by suitable closing mechanisms bywhich difierentparts of the basin can be eliminated from operation. The addition y ofv the inoculator-can also be accomplished by recirculation of a part ofthe decomposed solution or by subsequentclassiiication and recirculation of the fine hydrate portion.

.The basins for example can be made of concrete which could be covered by thin steel plate or by other suitable alkali-proof materials.

High costs for foundation of the heretofore known agitator tanks are not required. The agitating mechanism according to the present invention requires low investmentcosts and has a low power demand; Repairs can be done easily. The continuous operation can easily be supervisedand gives uniform results. l

g The manner of operating the present method ls illustrated by way of example in the attached quent settling zone and to prevent the settling of the precipitated aluminumhydroxide particles in the reaction zone.`

Itis a further object the.precipitation of the aluminumhydroxide particles from the aluminate liquor within the reacting zone by revolving agitation and to recirculate a bottom portion of the aluminumhydroxide particles loaded liquor to the feed inlet.

The invention may be advantageously carried out in a flat tank wherein by means of suitable agitating devices a horizontal main stream and near the bottom of the tank a secondary stream in opposite direction to the main stream is created which prevents the settling of the precipitated hydrate particles on the bottom of the tank below the agitating mechanisms and which aga n como'f-the inventiinto effect bines with the main stream o n the feed siV e of the tank at the upper level-of the liquid body.

drawing of which I Fig. 1 shows a' vertical section through the basin with agitating mechanism,l

' lig. 2 represents a top view.

The aluminate liquoris fed as top layer from the launder II into a fiat basin I2 which forms the decomposing or reaction zone. By the application of this zone of revolving agitation mechanisms two streams/I5, I4 are created which flow in diierent and opposite directions. The stream Il is the main stream of the liquid. The recir- 4cula-ted bottom stream I5 flowing in a direction opposite to the main stream is sulciently strong to prevent the settling of lhydrate of alumina on the bottom of the basin. The stream is created by the rotation of the paddle-wheels I6, I1, I8,

I9 which rotate in the same direction.

The fresh liquor emerging from the launder I IV hits the stream Il when entering the basin I2 and hereby reaches a zone ofhigh particle concentration I3. A major section of the solution continues to iiow through the basin and the aluminumhydroxide particles are transported into the settling zone at the end of the tankI where there are no agitator mechanisms.

Another portion of the stream I4 is deflected vstream I4. By this alteration of direction of the current continuously crystallization centers or nuclei are added to the fresh stream of solution whereby the precipitation of the hydrate of alumina is accelerated.

The tank I2 has a bottom 24, side walls 25,28 and a front wall 21. The discharge end of the basin is not shown in the drawing. Inside the basin the paddle-wheels I6 to I9 are arranged. The number and arrangement of these paddle wheels inside the tank can, of course, be varied in wide limits. Across the basin I2 are shafts 28 which may be supported on columns 29. In the shaft 28 is a sprocket 3I which `is driven .by a chain 32 and a sprocket 33 from the geared motor 34. The shaft 28 of thefpaddle-wheel I6 is provided with another sprocket `31. From this sprocket the sprockt 39 and the shaft 28 of the next paddle-Wheel I1 is driven by a chain 38. In

this way a single motor can be `used for driving all paddle-wheels.

The shaft 28 of the paddle-wheel I6 is provided with several arms 40, 4 I which carry the opposite paddles 42, 43. The paddle wheel I8 consists of several such units which are designated with A, B, C, D, E. Each paddle has diagonalrein- `forcing elements 44 which assist in the mixing procedure. The agitator mechanisms I6, I1, I8, I9 are of the same design with theonly difference that the paddles of the subsequent mechanism are staggered by 90. The paddles of. the mechanism I1 may be somewhat narrower `than those of mechanism I6. In the same way also paddles of mechanism I8 may be narrower lthanvthose of the mechanism I'I and those of the mechanism I 9 narrower than those of the mechanism I8.

Preferably the feed openingsv 23 should not be located lower than the horizontal plane in which the shafts 28 are situated. If these openings were located at a low level the incoming stream of solution would collide with the returning circulary stream.

The agitating mechanisms have to be arranged l sufficiently close to the bottom 24 so that no settling of particles on said `bottom may occur which may counteract the circular flow of the liquid.

I claim: l l. A fiocculation and sedimentation apparatus for aluminate liquors comprising a relatively long tank having a reaction space adjacent one end thereof and a settling space adjacent other end,

propelling means within the intermediate portion of the tank, said means including a plurality of paddles rotatable on a plurality of spaced shafts transversely perpendicular to the longitudinal axis of the tank, said paddles being located on a plane through the axis of the shafts, means to rotate said paddles in the same direction so that the paddles will rotate toward the settling space at the upper part of their rotational movementv and away from the settling space at the lower part of their rotational movement and means to feed aluminate liquor into the reaction space so that the said liquor will be seeded with precipitated particles returned to the reaction space by the paddles.

2. A flocculation and sedimentation apparatus for aluminate liquor comprising a relatively long tank containing liquid and having a reaction space adjacent one end thereof and a settling space adjacent the other end, propelling means within the intermediate portion of the tank consisting of paddles mounted on a plurality of horizontally rotatable shafts transversely placed with respect to the tank, and said paddles being located in a plane through the axis of the shafts, said shafts having means to rotate them all in the same. direction' so as-.to move liquid from the reaction space to the settling space at one level and to move liquid in the opposite direction at another level so that precipitated particles will be moved toward the settling space at the first level and portion thereof will be returned to the reaction space at the other level, said propelling means being constructed and arranged to move the liquid at a slower rate adjacent the settling space than adjacent the reaction space and means tofeed aluminate liquor into the reaction space `so that said liquor will be seeded with preclpitated particles.

3. A iiocculation and sedimentation apparatus for aluminate liquors comprising a'relatively long tank having a reaction space adjacent one end thereof and a settling space adjacent the other end, propelling means within the intermediate portion of the tank, said means including a plurality of paddles rotatable on a plurality of spaced shafts transversely perpendicular to the longitudinal axis ofthe tank, means to rotate said paddles inthe same direction so that the paddles will rotate toward the settling space at the upper part of their rotational movement and away from the settling space at the lower part of their rotational movement, the paddles adjacent the settling space being narrower than the paddles adjacent the reaction space, and means to feed aluminate liquor into the reaction space so that the said liquor will be seeded with precipitated particles returned to the reactionspace by the paddles.

HANS TIEDEMANN. 

